Night light lowers efficacy of breast cancer drug tamoxifen


Who's afraid of the dark? Breast cancer cells, apparently.

A study by researchers from Tulane University reveals that breast cancer treatment may be more effective when paired with sleeping in total darkness. Melatonin, a hormone produced in the pineal gland as a response mechanism to darkness, on its own can slow down the growth and significantly delay formation of tumors, but the inclusion of Tamoxifen leads to a drastic regression in test subjects.

Using rats implanted with breast cancer cells, the study was carried out in two phases. First, the rats were subjected to light and dark cycle where the test subjects were exposed to 12 hours of light and 12 hours of complete darkness. In the second phase of the study, the same light and darkness cycle was used but the rats were exposed to dim light equal in intensity to light coming from under a door during the darkness part of the cycle.

According to the study, high levels of melatonin during the night are capable of putting breast cancer cells to "sleep" by shutting down key growth mechanisms. Breast cancer cells are weak against Tamoxifen but somehow are able to "wake up" and resist the drug when there is light and levels of melatonin are down.

"Our data, although they were generated in rats, have potential implications for the large number of patients with breast cancer who are being treated with tamoxifen, because they suggest that night time exposure to light, even dim light, could cause their tumors to become resistant to the drug by suppressing melatonin production." explains co-leader of the Circadian Cancer Biology Group from Tulane University, Steven Hill.

He adds that the study, however, was not able to identify just how much light exposure was enough to suppress melatonin production during the night, although the researchers believe it can be as faint as light streaming from a street light.

Will taking melatonin supplements help?

Hill advises against the use of melatonin supplements because this has the potential to disrupt the natural sleep-wake cycle of a patient, interfering with the body's natural capability to produce the hormone. While melatonin is commonly thought of to be determined by sleep, exposure to darkness is actually more important. Sleep in a bright room and melatonin levels drop. Don't sleep but stay in a dark room and melatonin levels rise.

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